This invention relates in general to a touch control arrangement for use in graphics display apparatus and in particular to an improved light collector, or guide, for use in such an arrangement.
Graphics display apparatus, of the type herein considered, generally utilize a cathode ray tube (CRT), although other types of display devices can also be used. In any event, each of two adjacent edges of the display surface (faceplate) of the CRT is provided with a bank of light sources arranged to develop a group of parallel light beams which extend across the faceplate, the two groups intersecting, preferably at right angles. Like banks of light detectors flank those sides of the faceplate opposite an assigned bank of light sources.
In practice, a particular graphic is delivered for display by a controller in response to an operator's command which can take the form of a pointing to one area of the faceplate. This pointing serves to interrupt one or more of the light beams, which interruption causes the beam's assigned light detector to develop a signal which is applied to the controller to select the particular graphic. U.S. Pat. No. 3,775,560, for example, exemplifies this type display apparatus.
Display apparatus of the type adverted to above tend to be rather costly since a separate light sensor is employed with each light source. By way of reducing the number of light sensors, a novel light collecting arrangement is disclosed in co-pending application Ser. No. 408,096 filed on Aug. 13, 1982, now abandoned which application is a continuation-in-part of application Ser. No. 264,725 filed May 18, 1981 now abandoned. The '096 application discloses a light collection scheme which employs two sheets of light transmissive material such as plexiglass which are disposed on adjacent sides of the cathode ray tube's faceplate. The forward end of each sheet receives light from the bank of light sources disposed opposite thereto and directs such light to a light collection area at the opposite end of the sheet. In one embodiment, a light sensor is disposed at each light collection area. In a preferred embodiment, however, a single light sensor is utilized to respond to both light collection areas.
While this arrangement reduces the number of light sensors required to respond to a multitude of light sources, the configuration of the light collecting sheet poses problems insofar as the designs of the CRT's cabinet and escutcheon are concerned. In particular, the extent to which compactness can be achieved is subject to the overall size, as well as shape, of the light collectors.
Another problem which plagues graphics display apparatus of the type considered is the desensitization of the light detectors by strong ambient light sources. In bright rooms or in bright daylight, the ambient light can cause the apparatus to display erroneous information, or, in the worst case, to be rendered inoperative. This can occur when ambient light stimulates the light detectors to such an extent as to render the detectors insensitive to the desired light beams.